The present invention relates to a novel trueing and dressing tool for trueing and dressing grinding wheels. More particularly, the present invention relates to a method for trueing and dressing grinding wheels having vitrified-bonded cubic boron nitride (CBN) abrasive by using a reciprocating point trueing and dressing tool mounted between the head stock and tail stock of a cylindrical type grinding machine or on any suitable brake-controlled or powered rotary device for surface grinding machines.
A number of grinding wheels are known to those skilled in the art including, for example, conventional aluminum oxide and silicon carbide grinding wheels, resin-bonded and vitrified-bonded CBN grinding wheels, as well as, diamond grinding wheels. However, regardless of the type of abrasive employed in the grinding wheel, it is necessary to periodically true and dress the grinding wheel in order to maintain an open and aggressive grinding surface of a known profile. An open and aggressive surface condition is generally desirable since an open grinding wheel is less likely to burn a workpiece and requires less grinding power than a closed, or dull wheel.
A variety of methods for trueing and dressing grinding wheels are known in the art; however, each has various drawbacks and disadvantages, particularly in regard to trueing and dressing grinding wheels whose abrasive material is diamond or vitrified-bonded CBN. One prior art method is disclosed in U.S. Pat. No. 2,791,211 to Nagy and involves periodically indexing a diamond-tip dressing tool in relation to the grinding wheel so that in all indexing positions the diamond is in contact with the wheel in a direction of hard grain, forming an angle of between 30.degree. and 45.degree. to the crystal axis of the diamond. While such a single point diamond tool is effective for dressing conventional grinding wheels, such as aluminum oxide or silicon carbide, the diamond tip is subject to rapid wear and is generally ineffective for use in dressing grinding wheels employing diamond or vitrified-bonded CBN.
Another prior art method is disclosed in U.S. Pat. No. 4,866,887 to Imai, et al., and involves first trueing the grinding wheel with a trueing tool by making several passes across the grinding wheel at a relatively small infeed rate with a nib type dressing tool. In the final traverse feed, after the majority of the crown has been moved from the grinding wheel, the infeed rate of the trueing tool is set at a relatively larger value in order to form an aggressive cutting edge on the grinding wheel. A disadvantage of this method for trueing and dressing a grinding wheel appears from the number of cycles required in order to true the grinding wheel, as well as the expense involved in the central control unit used to control the infeed rates and positioning of the trueing and dressing tool. More importantly, such a tool is subject to rapid wear and loss of tool point geometry when used on diamond and vitrified-bonded CBN grinding wheels.
A number of alternatives to single point trueing and dressing tools are known in the art and include hand-set diamond and metal-bonded diamond rotary cup and straight wheel tools, as disclosed in U.S. Pat. No. 4,915,089 to Ruark, et al., which is assigned to the same assignee as the present invention and incorporated by reference into the present disclosure. While such rotary trueing and dressing tools have significantly longer life than single point tools, they are generally ineffective in generating the sharp, aggressive cutting surface on the grinding wheel produced by a single point dresser. Furthermore, they may require relatively expensive hydraulic or electric precision drive motors and spindle assemblies. Consequently, small machine shops are generally unable to avail themselves of rotary dressing technology. Another disadvantage of rotary cup wheel dressing tool technology is the necessity of periodically changing the position or angle of the dressing wheel in order to present new, sharper edges to the dressed wheel as the originally presented edges wear flat. Straight wheel dressing tools suffer from the further disadvantage of having the abrasive applied to the circumferential surface of the wheel in a band several millimeters in width. As a result, the operator has very little control over the dressed surface of the vitrified-bonded CBN or diamond grinding wheels because a wide band of abrasive, unlike a sharp point, generally leaves the wheel in a closed or dull condition. Wheels in such a dull condition are not desirable because they can generate excessive heat during the grinding process, which may cause the wheel to burn the workpiece. The powered rotary dressing tool as disclosed in Ruark, et al., while overcoming the disadvantage of the wide diamond width by its substitution of a single layer of diamond mounted in an axis perpendicular to the rotational axis of the dressing wheel, still requires a high degree of control over the rate of traverse to generate a sharp and open grinding wheel surface. In some cases, the rate of traverse required to generate an open wheel may exceed the physical capability of the grinding machine. Such additional traversing requirements may prohibit implementation or add an expense element to the trueing and grinding of diamond or vitrified-bonded CBN grinding wheels that would put the availability of such technology beyond the reach of small machine shops.
While such prior art methods may be considered acceptable, despite their respective shortcomings, manufacturers are always concerned with improving the trueing and dressing process, such as by reducing the time required to true and dress a grinding wheel to a sharp and open condition, reducing the costs of the trueing and dressing tool itself, and improving the quality of the profile of the trued grinding wheel surface.